14 



HYDROIDA II 



rings varies even within a single large colony to such a degree that the features in question cannot 

 be taken as distinctive specific characters, unless combined with others more sound. There remains 

 then the creeping form of colony. But Lafom fruticosa here differs in no wise from the remaining 

 species of the genus ; its colonies may be pure upright rhizocaulome formations, but this is very rarely 

 the case. Generally, the somewhat larger colonies consist partly of upright, partly of creeping por- 

 tions, and it is very common to meet with such composite colonies, when they are brought up with 

 the underlayer attached. Exclusively creeping colonies thus merely form the other extreme in the 



. - « b QO m. 



Fig. III. The distribution of Lafoea fruticosa forma gcnuina • and forma granJis -|- in the northern Atlantic. 



The hatched region denotes a common occurrence of Lafoea frulicosa according to literature. 



(In British waters the dates are to be revised owing to confusion of the species with Lafoea gracillima). 



same series of variants. Consequently therefore, Lafoea pocillum must be discarded, as being synony- 

 mous with Lafoea fruticosa. 



Jaderholm (1909 p. 71) follows, stating no particular reason, the example of Nutting (1901 

 p. 175) and ascribes Lafoea pocillion to the genus Hchclla. Nutting, in his diagnosis of this genus, 

 states as follows: "Hydrothec£e . . . having their cavities separated from those of the stem by a partial 

 septum". Such septum or diaphragm is altogether lacking in the European specimens of Lafom 

 pocillum. 



It must not be forgotten, however, that the former species partly owe their existence to external 

 determining factors. Disregarding the creeping form of colony as opposed to the upright, the differ- 

 ences presented by the colonies in a less extensive material are considerable enough to warrant at 

 any rate temporary distinction of species, and it would in these cases be incorrect not to notice the 



